LSST Acquires 1.2-meter Calypso Telescope

Anna Spitz and Victor Krabbendam

The LSST project acquired the 1.2-meter Calypso Telescope from Edgar Smith in November. LSST will use the telescope in its current location on Kitt Peak to conduct unique scientific investigations in support of calibration plans and to prototype hardware and software components. In the future, LSST plans to move the telescope to Chile to use it for atmospheric monitoring.

Edgar O. Smith, a businessman and astrophysicist, led the Calypso development in the late 1990s. The team developed the state-of-the-art telescope for high-resolution imaging of globular clusters among other studies. The primary, secondary, and tertiary mirrors are all made of Corning ULE® and coated with aluminum. The telescope’s primary mirror is a thin meniscus design. The telescope has two cameras: a high resolution camera and a wide field camera with a 4096 x 4096 15 micron pixel, thinned and backside-illuminated CCD that covers a 9.8' square field of view. Finished in 2001, Calypso has operated as the only stand-alone private facility on Kitt Peak since that year. Dr. Smith offered very generous terms for LSST to take over the facility, and the project is pleased to be able to put the facility to good use now and in the future.

The scientific plans for Calypso focus on several long baseline time domain observing programs for the next few years. The goal is to develop a strategy for photometric calibration that will achieve better than 1% photometry by observing over long baselines and varying conditions. LSST will migrate or improve coordination of observing programs prototyped at Cerro Tololo Inter-American Observatory, Kitt Peak, and Mt. Bigelow to Calypso to achieve a more comprehensive calibration investigation.

The team will use Calypso to measure stars with known spectral energy distribution over the entire visible sky, every 5-10 minutes, and several nights per lunar cycle over multiple observing seasons. From these data, LSST scientists will generate temporally and spatially dependent extinction maps of the atmospheric color terms. They will combine these spectral measurements with simultaneous photometric measurements of stars surrounding the spectral reference star. These measurements, in conjunction with the gray extinction measurements on scales from a few arc minutes to several degrees, will allow LSST to establish a new grid of photometric reference stars across the whole sky. These measurements are needed to know precisely the magnitude of these variations over the expected range of observing conditions that LSST will likely experience. While 1.6 magnitudes of extinction is clearly recognized as poor observing conditions, subtle cloud structure is not so easy to spot, but does materially affect the programs aiming for sub 1% photometry such as LSST.

In order to carry out this program, Calypso will need spectroscopic capability. LSST engineers will replace the high-resolution camera with a new small imaging, moderate resolution instrument and will also place LSST filters on the wide field imager. LSST has established professional services agreements with principals of the observatory to ensure the smooth handover of design and operational knowledge and encourage participation in development of new instrument plans.

Once moved to Cerro Pachón, Calypso’s atmospheric monitoring will provide additional contributions to LSST calibration. Observations with Calypso promise to bring important information for LSST’s calibration and as well as nice scientific results useful to the general community.